# ERR\_BUILD\_M3\_CACHE: Failed to build cache for Mautic 3. All your data has been successfully migrated to Mautic 3, but this error very likely needs to be fixed before you can start using Mautic 3 **URL:** \ **Category:** Mautic 3 - Install/Upgrade Support\ **Created:** [August 8, 2020, 7:50pm UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569 "2020-08-08T19:50:50Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![xadriano](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/xadriano/32/494_2.png) [@xadriano](https://forum.mautic.org/u/xadriano)\ **Post date:** [August 8, 2020, 7:50pm UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/1 "2020-08-08T19:50:50Z")
**MAUTIC3** _My PHP version is_ : 7.3.6 _My MySQL/MariaDB version is_: 5.7.31 **Updating/Installing Errors** [2020-08-08 18:54:00] ERR\_BUILD\_M3\_CACHE: Failed to build cache for Mautic 3. All your data has been successfully migrated to Mautic 3, but this error very likely needs to be fixed before you can start using Mautic 3. Command output: // Clearing the cache for the prod environment with debug true In ClassExistenceResource.php line 181: Class “Mautic\CoreBundle\EventListener\CommonSubscriber” not found while loading “MauticPlugin\MauticCronTesterBundle\EventListener\ButtonSubscriber”. cache:clear [–no-warmup] [–no-optional-warmers] [-h|–help] [-q|–quiet] [-v|vv|vvv|–verbose] [-V|–version] [–ansi] [–no-ansi] [-n|–no-interaction] [-e|–env ENV] [–no-debug] [–] \*I am Updating mautic 2.16.3 for mautic 3 \*Upgrading Command Line _These errors are showing in the installer_ :ERR\_BUILD\_M3\_CACHE: Failed to build cache for Mautic 3. All your data has been successfully migrated to Mautic 3, but this error very likely needs to be fixed before you can start using Mautic 3. Command output: // Clearing the cache for the prod environment with debug true In ClassExistenceResource.php line 181: Class “Mautic\CoreBundle\EventListener\CommonSubscriber” not found while loading “MauticPlugin\MauticCronTesterBundle\EventListener\ButtonSubscriber”. _These errors are showing in the Mautic log_ : _These errors are showing in the upgrade\_log.txt file (located in the root of your Mautic instance when an upgrade has been attempted - ensure you remove or redact any sensitive data such as domain names in the file path)_ : **Your problem** Internal Server Error try to open mautic _My problem is_ : how to solve ? _Steps I have tried to fix the problem_ : ---
**Author:** ![devsrealm](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/devsrealm/32/3669_2.png) [@devsrealm](https://forum.mautic.org/u/devsrealm)\ **Post date:** [August 8, 2020, 10:26pm UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/2 "2020-08-08T22:26:27Z")
Try to delete the cache and retry ---
**Author:** ![imrodmartin](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/imrodmartin/32/1756_2.png) [@imrodmartin](https://forum.mautic.org/u/imrodmartin)\ **Post date:** [August 31, 2020, 6:27pm UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/3 "2020-08-31T18:27:40Z")
so… I hit this error today too… is there a solution to it? (I’ve deleted var/cache/prod several times) ERR\_BUILD\_M3\_CACHE: Failed to build cache for Mautic 3… next steps? ---
**Author:** ![devsrealm](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/devsrealm/32/3669_2.png) [@devsrealm](https://forum.mautic.org/u/devsrealm)\ **Post date:** [August 31, 2020, 8:05pm UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/4 "2020-08-31T20:05:38Z")
What is your upgrade log showing? ---
**Author:** ![imrodmartin](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/imrodmartin/32/1756_2.png) [@imrodmartin](https://forum.mautic.org/u/imrodmartin)\ **Post date:** [September 2, 2020, 1:16pm UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/5 "2020-09-02T13:16:27Z")
[2020-08-31 18:10:24] Done! Your user data has been restored. Your Mautic 3 installation is ready. Just one more thing: [2020-08-31 18:10:24] Cleaning up installation files that we no longer need… [2020-08-31 18:10:24] Cleaned up successfully! [2020-08-31 18:10:24] Building cache for Mautic 3… [2020-08-31 18:10:24] ERR\_BUILD\_M3\_CACHE: Failed to build cache for Mautic 3. All your data has been successfully migrated to Mautic 3, but this error very likely needs to be fixed before you can start using Mautic 3. Command output: // Clearing the cache for the prod environment with debug true In ClassExistenceResource.php line 181: Class “Mautic\CoreBundle\EventListener\CommonSubscriber” not found while loading “MauticPlugin\MauticRecaptchaBundle\EventListener\FormSubsc riber”. cache:clear [–no-warmup] [–no-optional-warmers] [-h|–help] [-q|–quiet] [-v|vv|vvv|–verbose] [-V|–version] [–ansi] [–no-ansi] [-n|–no-interaction] [-e|–env ENV] [–no-debug] [–] I’ve tried deleting the cache/prod folder… to no avail. Also - the last 10,000 lines in the error\_log are: 02-Sep-2020 13:30:39 UTC] ReflectionException: Class “Mautic\CoreBundle\EventListener\CommonSubscriber” not found while loading “MauticPlugin\MauticRecaptchaBundle\EventListener\FormSubscriber”. - in file /home/imrodmartin/info.imrodmartin.com/vendor/symfony/config/Resource/ClassExistenceResource.php - at line 181 (obviously coming from a form that can’t load on my blog) Any help would be appreciated! (I have training videos to make LOL) ---
**Author:** ![imrodmartin](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/imrodmartin/32/1756_2.png) [@imrodmartin](https://forum.mautic.org/u/imrodmartin)\ **Post date:** [September 6, 2020, 10:19pm UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/6 "2020-09-06T22:19:54Z")
anyone? - i’d appreciate any more thoughts 🙂 ---
**Author:** ![imrodmartin](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/imrodmartin/32/1756_2.png) [@imrodmartin](https://forum.mautic.org/u/imrodmartin)\ **Post date:** [September 7, 2020, 12:58pm UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/7 "2020-09-07T12:58:48Z")
ok… so it turns out that at some point I had installed the Mautic 2.x re-captcha plugin and it’s not compatible with M3. (CommonSubscriber was removed in M3). Huge thanks to a good friend who caught that at the bottom of the log file. ---
**Author:** ![imihandstand](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/imihandstand/32/1499_2.png) [@imihandstand](https://forum.mautic.org/u/imihandstand)\ **Post date:** [April 29, 2021, 11:55am UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/8 "2021-04-29T11:55:53Z")
Thank you for this information. I found this error too in my logs, because of the plugin “MauticExtendeeToolsBundle”. ---
**Author:** ![joeyk](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/joeyk/32/11164_2.png) [@joeyk](https://forum.mautic.org/u/joeyk)\ **Post date:** [April 29, 2021, 11:58am UTC](https://forum.mautic.org/t/err-build-m3-cache-failed-to-build-cache-for-mautic-3-all-your-data-has-been-successfully-migrated-to-mautic-3-but-this-error-very-likely-needs-to-be-fixed-before-you-can-start-using-mautic-3/15569/9 "2021-04-29T11:58:40Z")
Correct. All non M2 compatible plugins must be removed before upgrade. You can add the M3 version of these plugins afterwards.